1. Preface

In recent years, powder coatings (hereinafter referred to as powders) have gradually become the main substitute for solvent based paints due to their 4E (environmentally friendly, economical, efficient, and excellent performance) advantages, and have also become the largest application field for household appliances.

But as people's awareness of environmental protection and health deepens, powder coatings for household appliances are gradually promoting the development towards environmentally friendly direction. This article focuses on explaining the environmentally friendly polyester/polyimide (HAA) (also known as HAA type) powder system for household appliances.

2. Types of weather resistant powders for household appliances

There are three main systems for household appliance powders: epoxy/polyester hybrid system, weather resistant polyester/TGIC system, weather resistant polyester/Primid system, and a small amount of weather resistant polyurethane and acrylic system.

Household Electrical Appliances, Issue 8, 2010; Powder coating for household appliances; Detailed introduction of the application of various powder systems in household appliances.

Among them, the environmentally friendly weather resistant polyester/polyimide system HAA has always been a hot topic of global concern as an alternative to non environmentally friendly weather resistant polyester/TGIC systems.

According to the 2010 statistics of the powder coating industry, the distribution of powder coating varieties in China and globally.

2. In the weather resistant system, the proportion of polyester/TGIC systems in China and globally is not significantly different, and both have a downward trend; There is still a significant gap between China's HAA type weather resistant powder and the world, and the growth rate is also significantly different.

According to industry statistical data analysis, the Chinese and North American (US) markets are dominated by TGIC type powders. In 2009, TGIC type powders accounted for 23% and 37% respectively in China and North America, while HAA type powders accounted for only 7% in China.

There is basically no HAA type (mainly polyurethane powder) in the North American market, while the European market is dominated by HAA type, accounting for 29%, and TGIC type powder is very rare. In Japan, TGIC is basically banned, mainly in the form of polyurethane powder.

3. The driving force behind HAA type substitution

Triglycidyl isocyanurate (TGIC) is one of the earliest curing agents used for outdoor powders. Its three epoxy groups have high activity, high crosslinking density, and a rigid triazine heterocyclic structure on the molecular framework, making the coating have good weather resistance, heat resistance, and hardness.

However, TGIC is irritating and allergic to human skin and eyes, and can induce mutations in animal cells, altering certain structures of genes, and these changes are heritable.

In 1998, based on in-depth toxicological research on TGIC, the European Union decided to regulate and label powders containing TGIC as toxic, providing space for the development of other systems.

Therefore, in 2000, the new alternative crosslinking agent beta was basically solved- Some key application technology issues of hydroxyalkylamides (HAA), especially after a series of tailored polyester products were developed, led to a significant decline in polyester/TGIC in Europe for the first time.

But in some emerging countries, TGIC is still the preferred curing agent. The reason is that although HAA has made significant progress, there are still many problems that have not been well solved.

However, despite being a major country in powder development in China, it has not yet become a powder powerhouse due to gaps in technology, funding, and management. The research on the application of HAA type weather resistant powder and the importance and urgency of its substitution for polyester/TGIC systems in the upstream and downstream chains are still far from sufficient, resulting in the widespread application of HAA type being in its early stages. Therefore, the development of HAA type in China has a long way to go.

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4. With the increasing global attention to chemical safety and health issues, the toxicity of TGIC and the development of alternative technologies that comply with REACH regulations, Germany's GS certification, the US CPISA Act, and other requirements need to be given sufficient attention.

At the same time, with the promulgation of China's Clean Production Promotion Law, it is required that production enterprises continuously adopt improved designs, use clean energy and raw materials, adopt advanced production technology and equipment, improve management, reduce pollution from the source, and ultimately reduce or eliminate the harm to human health and the environment.

Among various weather resistant powder varieties, polyurethane powder is widely used in North America and Japan due to its excellent comprehensive performance, accounting for 40% to 50% of its total powder.

But due to its high price in China (3-5 times higher than TGIC and HAA types), the need to import raw materials, the difficulty of curing agent technology, and the production of odors, it is basically difficult to become the mainstream substitute for TGIC type in China.

Therefore, the alternative technology and price of HAA type in China are more suitable for the national powder situation. The author believes that it will become a necessary and inevitable choice, but it requires the cooperation of powder users, powder enterprises, and raw material manufacturers to promote the rapid and large-scale industrial application of HAA type.

4. The production situation of HAA in our country

Table 2 shows the market situation of weather resistant polyester curing agents (TGIC and HAA) for powder coatings in China in recent years.

5. Table 2 (excluding import volume) shows that the absolute amount of HAA curing agent in China is still relatively small, but it shows a relatively stable growth rate, with an average growth rate 10% higher than that of TGIC curing agent.

In addition, China's TGIC import volume is zero, while HAA imports (mainly from Taiwan) 200 tons/year to stabilize the production of high-end HAA powder.

5. HAA Introduction

β-  Hydroxyalkylamide is a compound containing multiple hydroxyl functional groups, with extremely low toxicity (oral LD50 in mice is only 1/20 of TGIC), no irritation, and no mutagenesis, thus demonstrating relatively obvious environmental and human health friendliness.

Because its hydroxyl group is located in theβ It is affected by N atoms and has four functional groups, with high activity and significantly reduced curing temperature.

Synthesis&beta- The main methods for hydroxyalkylamides are:

(1) The method involves the direct reaction of dicarboxylic acid with hydroxylamine, resulting in a mixture of amide and ester;

(2) By reacting hydroxyethanolamine with epoxyethane or chlorohydrin, a product with high purity can be obtained. But epoxyethane has a low boiling point and is unsafe;

(3) The synthesis of beta using alkyl esters and hydroxyethanolamines under alkaline catalysis is a process both domestically and internationally- The main method for producing hydroxyalkylamides initially had low yield and many by-products, but after process improvement, the yield and purity were significantly improved.

The appearance of the synthesized product is light yellow; White powder or granules, hydroxyl equivalent 82± 2g/eq, non-volatile matter≥ 99.0%, melting range of 120-130 ℃. HAA curing agent was first introduced by Rohm and Hass in the United States, with the brand number XL552 and domestic grades T105 or T105M. Its molecular structure

6. Comparison of Performance between TGIC and HAA Weathering Polyester

Table 3 compares the performance of TGIC, HAA, and their weather resistant powders. Table 3 compares the experimental results of powder formulations for household appliances and air conditioners. It can be seen from the table that HAA type powder has stronger reactivity than TGIC, can be cured at low temperatures (160 ℃/15min), has better stability of the powder storage layer than TGIC, comparable weather resistance to TGIC, and can be used for friction gun spraying. The amount of curing agent used is less than TGIC.

However, HAA type powder releases low molecular weight compounds during solidification, and the coating is too thick, which can easily cause pinholes. The over baking heat resistance is worse than TGIC, the coating turns yellow, the burning fixture is not thorough, and the corrosion resistance is poor. However, with the gradual improvement of domestic polyester matching with HAA, the emergence of improved curing agent T105M, degassing agent and other additives, the chemical resistance, heat resistance, coating and other properties of HAA type have been well improved, and the comprehensive performance can be fully comparable to TGIC type.

7. The significance of replacing HAA powder

One of the fatal properties of TGIC type powder, in addition to its gradually strict toxicity restrictions, is that its storage stability deteriorates rapidly and easily clumps during summer, long-distance, and long-term transportation (especially export), causing the powder to be unable to be sprayed and its performance to deteriorate;

After prolonged storage, the performance deteriorates rapidly and the mechanical properties decrease rapidly; Furthermore, under the requirement of energy conservation and carbon emissions reduction, the solidification temperature of TGIC powder is too high, which has gradually been recognized by powder customers as a value limitation of its comprehensive cost.

And HAA type powder precisely solves the storage and transportation problem of powder, while implementing HAA type to replace TGIC type does not require any changes to construction facilities, only reducing the temperature of the construction drying tunnel, thus greatly reducing energy consumption and carbon emissions.

Its long-term comprehensive cost and social benefits are very obvious. A spray coating line factory with 5 medium-sized lines only saves 2 million yuan in electricity consumption, and its production efficiency improvement is self-evident.

With the gradual tightening of restrictions on TGIC abroad, it is foreseeable that TGIC will become an increasingly non mainstream product, and the development of HAA type alternative varieties in China is in line with China's national conditions.

Especially in terms of personal health, energy conservation, and reducing carbon emissions, many powder users are already paying attention to the value of HAA powder, and the rapid development of HAA powder in China is just around the corner.

8. Application of HAA type environmentally friendly powder coating in household appliances

HAA type environmentally friendly powder coatings in China mainly started in the field of household appliances and have become the mainstream substitute for household appliance powders.

9. Conclusion

The replacement of TGIC powder coating with HAA environmentally friendly weather resistant powder coating has become an inevitable trend in China. It is not only a requirement for environmental protection and human health, but also an inevitable requirement for energy conservation, consumption reduction, and carbon emissions reduction.

Of course, although many powder companies in China still face significant difficulties in solving key issues such as corrosion resistance, yellowing resistance, and coating pinholes in HAA type powder coatings due to technological innovation, funding, and other issues.

But as long as the ambitious individuals in the industry chain (raw materials, manufacturing enterprises, and powder users) fully recognize the importance and urgency of replacing HAA environmentally friendly weather resistant powder coatings.

To take the lead in industry competition, lead the banner of environmental protection, energy conservation and consumption reduction, promote better development of the industry, and fulfill our responsibility for human environmental protection and health, we need to take practical actions and work together upstream and downstream. Technical issues will not be a problem at all, as evidenced by the successful domestic enterprises.